This project will investigate the development of visual depth perception in human infants. It has two main goals. The first is to determine whether depth perception is present in newborn infants. Four experiments will be conducted to achieve this goal. They will use habituation of looking procedures to investigate whether newborn infants can perceive an object's constant physical size despite a change in its distance and retinal image size, and an object's constant physical shape despite a change in its slant and retinal image shape. Because these abilities, called size and shape constancy, require depth perception, their existence in newborns would indicate that some degree of depth perception is present at birth. The second main goal is to conduct a systematic investigation of changes in depth perception during the first seven months of life, and to identify the major transition points in depth perception development. This investigation will focus on the visual information (i.e., the depth cues) that infants use to perceive objects' distances and three-dimensional shapes. The adult visual system uses many depth cues to perceive distance and shape, including kinetic cues produced by motion in the optic array, binocular disparity, and pictorial cues such as perspective and shading. Young infants, in contrast, appear to be insensitive to most of these depth cues. The existing data suggest the hypothesis that infants have rudimentary depth perception abilities bases exclusively on kinetic cues before 3 months of age, that binocular (stereoscopic) depth perception develops between 3 and 4 months, and that sensitivity to the pictorial depth cues first appears between 5 and 7 months. Several experiments are proposed to test this hypothesis. They will use reaching, habituation, and preferential looking measures to seek the earliest age at which infants can perceive objects' distances and shapes from each class of depth cue. If these experiments confirm that sensitivity to kinetic, binocular, and pictorial depth cues develops in a stage-like sequence, follow-up studies will explore the significance of this developmental pattern by investigation how the emergence of sensitivity to a wider range of depth cues affects the infant's ability to perceive the environment's three-dimensional layout. The ultimate goal is a detailed theory of the mechanisms and processes underlying infant depth perception and its development.